Adding CNAME record for a domain with subdomain
In this case your custom domain will look like
calendar.yourbusiness.com
Log in to your GoDaddy dashboard
Select your domain and go to DNS Records
Click Add New Record
Select CNAME as the Type
Add Name and Value
Click Save button
For more information refer official documentation
Adding CNAME record for a root domain
We cannot set a CNAME record for the root domain in GoDaddy.